In 2387, a star in close proximity to Romulus went supernova and threatened the galaxy. To stop the threat, AmbassadorSpock used red matter to create a black hole which consumed the star's energy. Before he could successfully carry out his mission, however, the supernova reached Romulus, destroying the planet and all of its inhabitants. Among those killed were the wife and unborn child of Nero, who swore vengeance against Spock, Vulcan, and the Federation for letting his world die. While Nero confronted Spock, both of their ships were pulled into the black hole which had consumed the star, sending them back in time and resulting in the creation of the alternate reality. (Star Trek)

Having a supernova threaten the entire galaxy is a physical impossibility under normal circumstances due to the laws of physics limiting its expansion rate to below the speed of light, and the expansion of the blast wave would result in it eventually dissipating, making it virtually impossible for it to cause severe damage to a warp-capable society such as the Romulan Star Empire, let alone the entire galaxy. This discrepancy was explained several different ways in non-canon works.

In the comic book series Star Trek: Countdown, this star and its system were named "Hobus". The comic explained that the star's galactic threat came from its unusual ability to transform anything it contacted into energy, which it then consumed, increasing its power and causing it to expand farther and faster throughout the galaxy.

The Star Treknovelization instead stated that the star had merely threatened systems in its own vicinity rather than the entire galaxy.

A third explanation appears in the backstory of Star Trek Online, which states that the shock wave propagated through subspace at faster-than-light speeds. Also in the game's back story, a scandal occurred several years later involving rumors that the Vulcan Science Academy knew about the instability of the star but did nothing until Spock attempted to save Romulus with the Jellyfish. The scandal resulted in several resignations and sowed seeds of distrust towards the Vulcans.

It was also confirmed by the Featured Episode series "Cloaked Intentions" that Remus was also destroyed. However, the Romulans and Remans still continue their prejudices towards each other. It is also revealed that the supernova was not a natural occurrence, but was engineered by then-PraetorTaris, who did so under orders from the Iconians (though she claims she was duped by her then-science officer, Hakeev of the Tal Shiar).

In the more recent reference bookStellar Cartography: The Starfleet Reference Library ("Stellar Cartography", p. 35), the explosion of Hobus was called a "subspace supernova". This event resulted in the destruction of the entire Romulan star system, with billions killed. The cause of the explosion was unclear. The star was located in the Beta Quadrant. There was some contention on where precisely the star was located. On p. 35, the star was located in the Romulan Neutral Zone. Yet, in the "Federation Historical Highlights, 2161-2385" and "Position of the Romulan Star Empire", the star was located "southeast" of Romulus and quite some distance from the Neutral Zone. On the "Position of the Romulan Star Empire", which was a map of the Romulan Empire – prepared by the Stellar Archive Artist Lsel Essik, from the Romulan Master Data Catalog, in 2366 – Hobus was identified as a Romulan system.